The factor in defining sound property includes a pitch, an intensity and a tone color of sound. The pitch of sound is determined by a musical interval and a frequency, and an audio frequency (20 Hz˜20 kHz) is generally divided into a high range component, a middle range component and a low range component.
A good sound balance can be achieved by uniformly including high range sound, middle range sound and low range sound without leaning of the sound to one side. The intensity of sound is associated with a dynamic range of a sound apparatus, and means a different width between a sound of little volume and a sound of large volume. And the tone color of sound is generated by a mode of sound and a harmonic tone.
The sound apparatus for reproducing sound as analog sound wave from a sound source includes a stereo audio comprised of an amplifier and a set of (two) speakers to realize stereo sound, a 2.1, 3.1, 4.1, 5.1 or 7.1-channel audio system comprised of a multi-channel amplifier and 3, 4, 5, 6 or 8 speakers, and a multi-amplifier audio system in which a plurality of amplifying circuits are provided and speakers for low-pitched sound, middle-pitched sound and high-pitched sound are respectively connected with a separate amplifier so as to amplify the sounds in accordance with an output frequency band.
Since the conventional stereo system or multi-channel and multi-amplifier system is focused on realizing the stereo sound, it is possible to excellently realize the stereo sound.
However, there is not a function of delicately controlling each bass, baritone and treble by frequency bands, which determines a tone color, and also since it can adjust only the bass and treble, it is difficult to realize a tone color that is desired by a listener. In other words, for example, in an existing audio system comprised of an amplifier and a set of (two) speakers, when the bass and treble are adjusted so as to control the low-pitched sound and high-pitched sound, if the bass is increased, a volume level of the low-pitched sound is increased, but volume levels of the middle-pitched sound and high-pitched sound are relatively reduced. And if the treble is increased a volume level of the high-pitched sound is increased, but volume levels of the low-pitched sound and middle-pitched sound are relatively reduced.
Thus, there are technical limitations that it is difficult to exhibit balanced sound, and sound field effect, realism and density of sound are also reduced. Even in the multi-channel and multi-amplifier system, there are technical limitations as described above.
Further, in the conventional audio system, if a volume of sound is increased, noise as well as sound is increased according to SNR (Signal to Noise Ratio) of an amplifier, and thus the whole sound becomes rough.
Furthermore, in the conventional audio system, since a user has to select one of a vacuum tube amplifier and a transistor amplifier and also select one of a closed type speaker and an open type speaker, it is difficult to realize sound having various tone colors.